Various structures have been developed for unloading trucks, most of these being power operated, including the techniques of tilting the box of the vehicle, provision of rollers on the floor of the box, and flexible conveyors incorporated in the floor of the box. The last mentioned structure is disclosed in several U.S. Pat. Nos., notably Flinchbaugh, 2,551,368; Claffey, 2,563,158 and Lavelle et al., 2,595,395 and Turner et al., 2,537,381. These patents show the simple concept of a conveyor in the floor of the vehicle box and this concept is recognized as well known prior art. Variation of such concept is noted in Carpenture Jr. et al., 3,704,798 where pallets are slung on overhead rails, in Simo, 2,808,159 where the conveyor is segmented and mounted on top of fixed rails, in Buye et al., 2,515,334 where a principal part of the box per se is open bottomed and moves rearwardly to discharge the load. None of this prior art discloses a load cover combined with the conveyor. The closest to this concept being Ford, U.S. Pat. No. 1,329,392 which patent shows a cable used to pull a rope-reinforced fabric rearwardly from the top front end as the vehicle is advanced in order to unload the box. No load covers except those of tie-down tarpaulin type are presently available and there is a need for a simple cover structure to protect the load especially loads susceptible to wind during transit.